Building on results of the previous five years of the Program, the research activities conducted under this project will be directed to identification and clinical application of scalp electrophysiological indices of vibrotactile adaptation and dynamic tactile/pain interactions in human somatosensory cortex. In years 11-12 of the proposed research, intensive experimental studies will continue on a small sample of neurologically normal adults to identify and characterize EEG signs of normal vibrotactile adaptation and their relationship to psychophysical effects previously identified by Project 2 (Hollins). Further within-subject studies in years 12-13 will explore effects of an NMDA receptor blocker (Dextromethorphan) and concurrent thermal pain or capsaicin-induced hyperpathic pain on the normal course of vibrotactile adaptation. I addition to their basic- research interest, these experiments will enable us to identify stimulus protocols and response measurement techniques that can provide robust quantitative indices of somatosensory cortical adaptation suitable for application in a clinical setting. The second phase of the research in years 14-15 will use these indices for experimental study of hypothesized disturbances of somatosensory cortical dynamics in an orofacial sensory dysfunction group (TMD patients). The research is expected to lead to improved electrophysiological characterization of both normal and disturbed somatosensory cortical dynamics. The neurophysiological measures developed will complement the psychophysical ones under development in the Program's other subprojects, and thus provide additional means both for detecting and characterizing deficits and for monitoring the effects of treatment and the progress of recovery. In addition, the experimental results should help to establish a firm neuroscientific foundation for clinically useful psychophysical and behavioral measurements in humans, by providing interpretive bridges between these measurements and the more detailed observations available from prior neurophysiological studies of somatosensory cortical mechanisms in animal subjects.